Catheter with bendable tip

ABSTRACT

A medical probe includes a flexible insertion tube, having a distal end for insertion into a body cavity of a patient, and a distal tip, which is disposed at the distal end of the insertion tube and is configured to be brought into contact with tissue in the body cavity. A coupling member couples the distal tip to the distal end of the insertion tube and includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece.

FIELD OF THE INVENTION

The present invention relates generally to invasive medical devices, andspecifically to the construction of probes for insertion into bodyorgans.

BACKGROUND OF THE INVENTION

In some diagnostic and therapeutic techniques, a catheter is insertedinto a chamber of the heart and brought into contact with the innerheart wall. In such procedures, it is generally important that thedistal tip of the catheter engages the endocardium with sufficientpressure to ensure good contact. Excessive pressure, however, may causeundesired damage to the heart tissue and even perforation of the heartwall.

For example, in intracardiac radio-frequency (RF) ablation, a catheterhaving an electrode at its distal tip is inserted through the patient'svascular system into a chamber of the heart. The electrode is broughtinto contact with a site (or sites) on the endocardium, and RF energy isapplied through the catheter to the electrode in order to ablate theheart tissue at the site. Proper contact between the electrode and theendocardium during ablation is necessary in order to achieve the desiredtherapeutic effect without excessive damage to the tissue.

A number of patent publications describe catheters with integratedpressure sensors for sensing tissue contact. As one example, U.S. PatentApplication Publication 2007/0100332, whose disclosure is incorporatedherein by reference, describes systems and methods for assessingelectrode-tissue contact for tissue ablation. An electro-mechanicalsensor within the catheter shaft generates electrical signalscorresponding to the amount of movement of the electrode within a distalportion of the catheter shaft. An output device receives the electricalsignals for assessing a level of contact between the electrode and atissue.

SUMMARY OF THE INVENTION

The embodiments of the present invention that are described hereinbelowprovide a novel design of an invasive probe, such as a catheter. Theprobe comprises a flexible insertion tube, having a distal end forinsertion into a body cavity of a patient. The distal tip of the probeis coupled to the distal end of the insertion tube by a coupling member.The coupling member comprises a tubular piece of an elastic material,such as a superelastic alloy, with a helical cut running along a portionof the length of the piece.

The coupling member permits the distal tip to bend in response topressure exerted on the distal tip when the distal tip engages tissue inthe body cavity. Typically, the bend angle is proportional to thepressure and may be measured in order to determine the force of contactbetween the probe and the tissue. On the other hand, the width of thehelical cut may be chosen so as to inhibit bending of the distal tipbeyond a certain angular limit in order to avoid damaging the probe.

There is therefore provided, in accordance with an embodiment of thepresent invention, a medical probe, including:

a flexible insertion tube, having a distal end for insertion into a bodycavity of a patient;

a distal tip, which is disposed at the distal end of the insertion tubeand is configured to be brought into contact with tissue in the bodycavity; and

a coupling member, which couples the distal tip to the distal end of theinsertion tube and includes a tubular piece of an elastic materialhaving a helical cut therethrough along a portion of a length of thepiece.

In a disclosed embodiment, the elastic material includes a superelasticalloy, and the helical cut subtends an angle between 360° and 720° aboutan axis of the tubular piece.

Typically, the coupling member is configured to bend in response topressure exerted on the distal tip when the distal tip engages thetissue, and the helical cut has a width chosen so as to inhibit bendingof the distal tip beyond a predetermined angular limit.

In some embodiments, the probe includes a position sensor within thedistal tip, wherein the position sensor is configured to sense aposition of the distal tip relative to the distal end of the insertiontube, which changes in response to deformation of the coupling member.In a disclosed embodiment, the position sensor is configured to generatea signal in response to a magnetic field, wherein the signal isindicative of a position of the distal tip. The probe may include amagnetic field generator within the distal end of the insertion tube forgenerating the magnetic field. Additionally or alternatively, the probeincludes an electrical conductor, which is coupled to a distal side ofthe position sensor and is curved to pass in a proximal direction aroundthe position sensor and through the insertion tube so as to conveyposition signals from the position sensor to a proximal end of theinsertion tube.

In some embodiments, the probe includes a pull-wire for use by anoperator of the probe in steering the probe, wherein the pull-wirepasses through the insertion tube and is anchored at a point in thedistal end of the insertion tube that is proximal to the helical cut inthe coupling member. Alternatively or additionally, the probe includes aheat-resistant plastic sheath covering at least the coupling member.

In a disclosed embodiment, the insertion tube, distal tip and couplingmember are configured for insertion through a blood vessel into a heartof a patient.

There is also provided, in accordance with an embodiment of the presentinvention, a method for performing a medical procedure, including:

inserting into a body cavity of a patient a probe, which includes aflexible insertion tube and a distal tip, which is disposed at a distalend of the insertion tube, and a coupling member, which couples thedistal tip to the distal end of the insertion tube and includes atubular piece of an elastic material having a helical cut therethroughalong a portion of a length of the piece; and

bringing the distal tip into contact with tissue in the body cavity.

In a disclosed embodiment, inserting the probe includes passing theprobe through a blood vessel into a heart of the patient, and the methodincludes ablating the tissue with which the distal tip is in contact.

There is additionally provided, in accordance with an embodiment of thepresent invention, a method for producing a medical probe, including:

providing a flexible insertion tube, having a distal end for insertioninto a body cavity of a patient, and a distal tip, which is configuredto be brought into contact with tissue in the body cavity; and

coupling the distal dip to the distal end of the insertion tube using acoupling member, which includes a tubular piece of an elastic materialhaving a helical cut therethrough along a portion of a length of thepiece.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a heart chamber with a catheterin contact with the heart wall inside the chamber, in accordance with anembodiment of the present invention;

FIG. 2 is a schematic sectional view of a catheter, in accordance withan embodiment of the present invention; and

FIG. 3 is a schematic side view of a coupling member, in accordance withan embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic sectional view of a chamber of a heart 22, showingan insertion tube 26 of a catheter 20 inside the heart, in accordancewith an embodiment of the present invention. The catheter is typicallyinserted into the heart percutaneously through a blood vessel, such asthe vena cava or the aorta. An electrode 28 on a distal tip 24 of thecatheter engages endocardial tissue 30. Pressure exerted by the distaltip against the endocardium deforms the endocardial tissue locally, sothat electrode 28 contacts the tissue over a relatively large area. Inthe pictured example, the electrode engages the endocardium at an angle,rather than head-on. Distal tip 24 therefore bends at an elastic joint32 relative to the insertion tube of the catheter. The bend facilitatesoptimal contact between the electrode and the endocardial tissue.

Because of the elastic quality of joint 32, the angle of bending of thejoint is proportional to the pressure exerted by tissue 30 on distal tip24 (or equivalently, the pressure exerted by the distal tip on thetissue). Measurement of the bend angle thus gives an indication of thispressure. The pressure indication may be used by the operator ofcatheter 20 is ensuring that the distal tip is pressing against theendocardium firmly enough to give the desired therapeutic or diagnosticresult, but not so hard as to cause undesired tissue damage. U.S. patentapplication Ser. No. 11/868,733, filed Oct. 8, 2007, whose disclosure isincorporated herein by reference, describes a system that uses apressure-sensing catheter in this manner. Catheter 20 may be used insuch a system.

FIG. 2 is a schematic, sectional view of catheter 20, showing details ofthe distal end of the catheter, in accordance with an embodiment of thepresent invention. A coupling member 40 forms the joint between distaltip 24 and the distal end of insertion tube 26. The coupling member hasthe form of a tubular piece of an elastic material, with a helical cutalong a portion of its length, as shown more particularly in FIG. 3.Typically, the coupling member (along with the distal end of catheter 20generally) is covered by a flexible plastic sheath 42. When catheter 20is used, for example, in ablating endocardial tissue by delivering RFelectrical energy through electrode 28, considerable heat is generatedin the area of distal tip 24. For this reason, it is desirable thatsheath 42 comprise a heat-resistant plastic material, such aspolyurethane, whose shape and elasticity are not substantially affectedby exposure to the heat.

Catheter 20 comprises a position sensor 44 within distal tip 24. (In thepictured embodiment, the position sensor is contained within a part ofcoupling member 40 that is inside the distal tip of the catheter.) Theposition sensor is connected via a conductor 46 to a processing unit(not shown) at the proximal end of insertion tube 26. Conductor 46 maytypically comprise a twisted-pair cable. Position sensor 44 isconfigured to sense the position of the distal tip relative to thedistal end of the insertion tube. As explained above, this positionchanges in response to deformation of the coupling member, and theprocessing unit may thus use the position reading in order to give anindication of the pressure exerted on and by the distal tip.

For intracardiac operation, insertion tube 26 and distal tip 24 shouldgenerally have a very small outer diameter, typically on the order of2-3 mm. Therefore, all of the internal components of catheter 20, suchas conductor 46, are also made as small and thin as possible and arethus susceptible to damage due to even small mechanical strains. Toavoid damage to conductor 46 when coupling member 40 bends, theconductor is coupled to the distal side of position sensor 44, as shownin FIG. 2, rather than to the proximal side, from which the path of theconductor would be shorter. The conductor is then curved to pass in aproximal direction around the position sensor and through insertion tube26 so as to convey position signals from the position sensor to theprocessing unit via the proximal end of the insertion tube.

Position sensor 44 may comprise one or more coils, which are configuredto generate signals in response to a magnetic field. These signals areindicative of the position and orientation of distal tip 24. Themagnetic field may be produced by a miniature magnetic field generator48 within the distal end of the insertion tube. Thus, when couplingmember 40 bends, the signals generated by the position sensor change andcan be analyzed by the processing unit to determine the pressure on thedistal tip. Additional magnetic fields may be generated by fieldgenerators (not shown) in fixed locations external to the patient'sbody. These fields cause position sensor 44 to generate additionalsignals that are indicative of the position and orientation of distaltip 24 in the fixed frame of reference of the external field generators.These aspects of the operation of position sensor 44 are described indetail in the above-mentioned U.S. patent application Ser. No.11/868,733. They are outside the scope of the present invention.

Catheter 20 may comprise a pull-wire 50 for use by an operator insteering the catheter. The pull-wire passes through insertion tube 26and is anchored at an anchor point 52 in the distal end of the insertiontube. The operator tightens the pull-wire (typically by turning aknob—not shown—at the proximal end of the catheter) in order to bend thedistal end of the catheter. When the operator releases the pull-wire,the catheter straightens due to the resilience of the insertion tube. Incatheters that are known in the art, the pull-wire is anchored near thedistal tip of the catheter. In catheter 20, however, anchor point 52 isproximal to the helical cut in coupling member 40, and may be proximalto the coupling member altogether, as shown in FIG. 2. This relativelyproximal positioning of the anchor point means that the pull-wire steersthe catheter as a whole, rather than bending the coupling member anddistal tip.

FIG. 3 is a schematic side view of coupling member 40, in accordancewith an embodiment of the present invention. As noted earlier, thecoupling member comprises a tubular piece 60 of an elastic material,typically a metal material. For example, the coupling member maycomprise a superelastic alloy, such as nickel titanium (NITINOL). Forintracardiac applications, the NITINOL tube may typically have a lengthof 10 mm, with outer diameter 2.0 mm and wall thickness 0.05 mm.Alternatively, in other applications, the tube may have larger orsmaller dimensions.

A helical cut 62 is made along a portion of the length of tubular piece60, and thus causes the tubular piece to behave like a spring inresponse to forces exerted on distal tip 24. Cut 62 may be made by lasermachining of the tubular piece. For the tube dimensions given above, cut62 is typically opened by the laser to a width of about 0.1 mm. To givethe appropriate balance between flexibility and stiffness forintracardiac applications, cut 62 typically subtends an angle between360° and 720° about the central axis of the tubular piece, asillustrated in FIG. 3 (in which the cut subtends about 540°).Alternatively, larger or smaller angular extents may be used dependingon application requirements.

The spring-like behavior of coupling member 40 extends up to a certainangle of bending of tubular piece 60, for example, 30°. Above thisangle, the sides of cut 62 on the inner side of the bend will come intocontact, thereby inhibiting any further bending of the distal tip. Thewidth of the cut may thus be chosen so as to impose a predeterminedangular limit on the bending of joint 32 (FIG. 1). This sort of bendlimit is useful in preventing damage that may occur to the delicateinternal components of catheter 20 due to excessive bending.

Although the operation and construction of catheter 20 are describedabove in the context of catheter-based intracardiac procedures, theprinciples of the present invention may similarly be applied in othertherapeutic and diagnostic applications that use invasive probes, bothin the heart and in other organs of the body. Furthermore, theprinciples of the implementation of catheter 20 and coupling member 40may also be applied to enhance flexibility in catheter designs of othertypes, such as lasso, helix, and “Pentarray” type catheters. In ahelical lasso catheter, for example, resilient elements like couplingmember 40 may be incorporated in the helix in order to enhance the easeof use and accuracy of alignment of the lasso in the desired positionwithin the heart.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsubcombinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art.

The invention claimed is:
 1. A medical probe, comprising: a flexibleinsertion tube, having a distal end for insertion into a body cavity ofa patient, the insertion tube comprising a magnetic field generatorwithin the distal end of the insertion tube for generating a magneticfield; a distal tip, which is disposed at the distal end of theinsertion tube and is configured to be brought into contact with tissuein the body cavity, the distal tip comprising a position sensor withinthe distal tip, wherein the position sensor is configured to generate asignal in response to the magnetic field, and wherein the signal isindicative of a position of the distal tip; and a coupling member, whichcouples the distal tip to the distal end of the insertion tube andcomprises a tubular piece of an elastic material having a helical cuttherethrough along a portion of a length of the piece.
 2. The probeaccording to claim 1, wherein the elastic material comprises asuperelastic alloy.
 3. The probe according to claim 1, wherein thehelical cut subtends an angle between 360° and 720° about an axis of thetubular piece.
 4. The probe according to claim 1, wherein the couplingmember is configured to bend in response to pressure exerted on thedistal tip when the distal tip engages the tissue, and wherein thehelical cut has a width chosen so as to inhibit bending of the distaltip beyond a predetermined angular limit.
 5. The probe according toclaim 1, wherein the position sensor is configured to sense a positionof the distal tip relative to the distal end of the insertion tube,which changes in response to deformation of the coupling member.
 6. Theprobe according to claim 1, and comprising an electrical conductor,which is coupled to a distal side of the position sensor and is curvedto pass in a proximal direction around the position sensor and throughthe insertion tube so as to convey position signals from the positionsensor to a proximal end of the insertion tube.
 7. The probe accordingto claim 1, and comprising a pull-wire for use by an operator of theprobe in steering the probe, wherein the pull-wire passes through theinsertion tube and is anchored at a point in the distal end of theinsertion tube that is proximal to the helical cut in the couplingmember.
 8. The probe according to claim 1, and comprising aheat-resistant plastic sheath covering at least the coupling member. 9.The probe according to claim 1, wherein the insertion tube, distal tipand coupling member are configured for insertion through a blood vesselinto a heart of a patient.